期刊名称:Proceedings of the National Academy of Sciences
印刷版ISSN:0027-8424
电子版ISSN:1091-6490
出版年度:1998
卷号:95
期号:25
页码:14622-14627
DOI:10.1073/pnas.95.25.14622
语种:English
出版社:The National Academy of Sciences of the United States of America
摘要:Recently, cryoelectron microscopy of isolated macromolecular complexes has advanced to resolutions below 10 A, enabling direct visualization of -helical secondary structure. To help correlate such density maps with the amino acid sequences of the component proteins, we advocate peptide-based difference mapping, i.e., insertion of peptides, {approx}10 residues long, at targeted points in the sequence and visualization of these peptides as bulk labels in cryoelectron microscopy-derived difference maps. As proof of principle, we have appended an extraneous octapeptide at the N terminus of hepatitis B virus capsid protein and determined its location on the capsid surface by difference imaging at 11 A resolution. Hepatitis B virus capsids are icosahedral particles, {approx}300 A in diameter, made up of T-shaped dimers (subunit Mr, 16-21 kDa, depending on construct). The stems of the Ts protrude outward as spikes, whereas the crosspieces pack to form the contiguous shell. The two N termini per dimer reside on either side of the spike-stem, at the level at which it enters the shell. This location is consistent with formation of the known intramolecular disulfide bond between the cysteines at positions 61 and -7 (in the residual propeptide) in the "e-antigen" form of the capsid protein and has implications for why this clinically important antigen remains unassembled in vivo.
关键词:hepatitis B virus core antigen/virus capsid structure/three-dimensional image reconstruction